The incident happened on Bromley High Street just before 4.20pm today (August 3).
Officers, London Ambulance Service crews and an air ambulance attended.
The man was found injured nearby in Harmony Way.
He was treated before being taken to hospital where his condition was assessed as not life-threatening.
No arrests have been made as police enquiries continue.
A spokesperson for Metropolitan Police said: “Police were called at 16:18hrs on Saturday, 3 August to reports of a stabbing in High Street, Bromley.
“Officers responded with LAS and London’s Air Ambulance.
“The victim, aged 19, was found near Harmony Way.
“He was treated before being taken to hospital, where his condition was later assessed as not life-threatening.
“There have been no arrests at this time.
“A crime scene is in place.”
